Two sounds separated by a brief interval are perceived as a single auditory image located near the lead stimulus. This property has been termed the "precedence effect" and is thought to be important for suppressing echoes when listening in reverberant environments. A complete understanding of the neural mechanisms underlying the precedence effect may lead to improvements in the design of binaural hearing aids and prosthetic devices that must operate in such environments. We propose to study these mechanisms in the inferior colliculus (IC), which is an important point of convergence in the ascending auditory system. When presented with two clicks separated by a delay, most neurons in the central nucleus of the IC show suppressed responses to the second click. This study seeks to identify which of these suppressive responses actually underlie the precedence effect. Specifically, responses to precedence effect stimuli will be segregated based on the origins of the afferent fibers that converge to shape those responses. The techniques will combine extracellular physiology and microinjections of the anatomical tracer Neurobiotin. Models will be developed to assess the ability of each identified subpopulation to predict psychophysical performance under precedence effect conditions. The data obtained will help identify more precisely the strategies employed by the auditory system to localize sound in complex acoustic environments.